The present invention relates to a DNA probe for identifying bacterial strains of the Lactobacillus delbrueckii species, a process for producing such a probe and methods for identifying bacterial strains of this species with this DNA probe.
Lactobacillus delbrueckii subsp. bulgaricus, delbrueckii and lactis are very important bacteria for the fermentation of food. L. bulgaricus and L. lactis are predominantly used in fermentation of milk products and are therefore found in starter cultures for yoghurt and cheese production, whereas L. delbrueckii is mainly found in vegetable fermentations. Fermentation and maturation of these food products usually result from growth association and interaction of different bacteria, in most cases different Lactobacilli, Lactococci and other bacterial species. As most of these bacterial species have very similar nutritional requirements and grow under similar environmental conditions, a clear identification within the Lactobacillus species is sometimes very difficult. So far the classification of these species is very tedious and involves many unreliable criteria like sugar fermentation patterns and acid production. Due to these tests, a differentiation of different species remains difficult, sometimes doubtful and often arbitrary.
DNA hybridisation techniques, using specific DNA probes are a very valuable tool for the identification of bacterial and viral strains and have already found application in clinical diagnostics. Such DNA probes have already been used for the identification of Yersinia enterocolitica (J. Jagow et al., Appl. Environ. Microbiol. 51, 441-443, 1986), Plasmodiurn falciparum (R. H. Barker et al. Science 231, 1434-1436, 1986), Salmonella typhi (F. A. Rubin et al., J. Clin. Microbiol. 22, 600-605, 1985), Bacillus subtilis (J. Krauss et al., FEMS Microbiol. Lett. 33, 89-93, 1986), Haemophilus influenzae (F. Malouin et al., J. Clin. Microbiol. 26, 2132-2138, 1988) and other bacterial species, of DNA viruses (J. Brandsma et al., Proc. Natl. Acad. Sci. USA 77, 6851-6855; P. Stolhandske et al., J. Clin. Microbiol. 15, 744-747, 1982; P. Stolhandske et al., J. Med. Virol. 12, 213-218,1985), as well as RNA viruses (J. Flores et al., Lanceti, 555-559, 1983; M. Lin et al., J. Virol. 55, 509-512, 1985).
In the species of Lactobacillus, only a probe for L. curvatus (H. A. R. Petrick et al, Appl. Environ. Microbiol. 54, 405-408, 1988), which is specifically associated with spoilage of vacuum-packed meats, has been isolated. It certainly would be of use in the dairy industry to have a quick and reliable method to identify and classify relevant strains of the lactic acid bacteria.